Operation of a mold block with air flow control

ABSTRACT

A mold block which is used in a moving mold tunnel comprises first and second mold block sections which meet at their parting faces to close the mold block. Each mold block section has a product shaping interior surface and an air movement passage having an entrance at the base of each mold block section, a first opening to the interior surface and a second opening to the parting face of each mold block section. An air flow controller is provided between the parting face opening and the interior surface opening of the passage in the first mold block section and an air flow controller is provided between the entrance and the interior surface opening in the passage in the second mold block section. Through various different positionings of the two air flow controllers, the mold block can be operated in any one of four different modes including a first vacuum forming mode in which air is withdrawn from the mold block through both of the mold block sections, a second vacuum forming mode in which air is withdrawn from the mold block through only one of the mold block sections, a third cooling mode in which air is introduced into the mold block through one of the mold block sections and is then withdrawn from the other of the mold block sections and a fourth blow molding mode in which pressure within the mold block is released through both mold block sections.

This is a Divisional application of application Ser. No. 09/048,088filed on Mar. 26, 1998, now U.S. Pat. No. 6,089,851.

FIELD OF THE INVENTION

The present invention relates to a mold block which is used in a movingmold tunnel and which is particularly useful in the molding of profiledplastic pipe.

BACKGROUND OF THE INVENTION

Corma Inc. of Toronto, Ontario, Canada has for many years beenmanufacturing and selling plastic pipe molding equipment. This equipmentincludes mold block sections circulating on endless tracks and meetingwith one another to form complete mold blocks which are carried along amoving mold tunnel. The Corma mold blocks feature slit-like openings onthe interior surfaces of the mold blocks which provide openings fordrawing air out of the mold blocks. These vacuum slit bearing moldblocks have proved extremely efficient in the vacuum forming of plasticpipe where the vacuum has been induced from both mold block sections.They have also, to a lesser extent, been used in the blow molding ofpipe.

To date, the Corma mold block has not been used for cooling purposeswhere it is very important to provide cooling of both the pipe and themold blocks used in making the pipe. Such cooling substantiallyincreases production speeds of the pipe mold.

SUMMARY OF THE INVENTION

It has now been discovered that by providing air flow controls atspecified locations a mold block of the type described above can be usednot only as it has been in the past, but for additional purposes aswell.

More particularly, a mold block which is used with like mold blocks in amoving mold tunnel comprises first and second mold block sections, eachof which has an air movement passage which includes an entrance, a firstopening to the product shaping interior surface and a second opening tothe parting face of each mold block section. When the two mold blocksections are closed with one another at their parting faces, the partingface opening in the first mold block section meets with the parting faceopening in the second mold block section.

Also provided are first and second air flow controllers which aremovable independently of one another between an air flow and an airblocking position. The first air flow controller is located between theparting face opening and the interior surface opening in the passage inthe first mold block section and the second air flow controller islocated between the entrance and the interior surface opening in thepassage in the second mold block section.

A mold block as described above can be used in any one of four differentmodes of operation including a first vacuum forming mode in which air iswithdrawn from the mold block through both mold block sections, a secondvacuum forming mode of operation in which air is withdrawn from the moldblock through only one of the mold block sections, a third cooling modeof operation in which air is introduced to the mold block through onemold block section and is withdrawn from the mold block through theother mold block section, and a fourth blow molding mode in which airpressure is released from the mold block through both mold blocksections.

In accordance with the present invention, a mold block having air flowcontrollers as described immediately above, has substantially enhancedversatility over the known Corma mold block.

BRIEF DESCRIPTION OF THE DRAWINGS

The above as well as other advantages and features of the presentinvention will be described in greater detail according to the preferredembodiments of the present invention in which;

FIG. 1 is a schematic view of a pipe molding apparatus;

FIG. 2 is an enlarged perspective view of separated mold block sectionswhich meet at their parting faces to form a mold block according to apreferred embodiment of the present invention;

FIGS. 3 through 6 are sectional views through the mold block formed bythe mold block sections of FIG. 2 showing the various different modes ofoperation of the mold block;

FIG. 7 is a perspective view of the air flow control region of one ofthe mold block sections of FIG. 2 and also showing a specific type ofair flow controller usable in the air flow control region according to apreferred embodiment of the present invention;

FIG. 7a is a view similar to FIG. 7 showing an alternate form of an airflow controller according to a further preferred embodiment of thepresent invention;

FIGS. 8 and 9 are sectional views through a simplified mold blockshowing different positions of operation of the air flow controller ofFIG. 7.

DETAILED DESCRIPTION ACCORDING TO THE PREFERRED EMBODIMENTS OF THEPRESENT INVENTION

FIG. 1 shows a pipe molding apparatus generally indicated at 1. Thisapparatus comprises an extruder 3 which feeds molten plastic in adownstream direction to a pipe mold for forming profiled pipe generallyindicated at P. The pipe mold is formed by upper and lower sets of moldblock sections 3 and 4 each of which are carried around an endless trackas shown in FIG. 1. Where the mold block sections meet with one another,they form a moving mold tunnel generally indicated at 5.

FIG. 2 shows in greater detail the two mold block sections 3 and 5 whichmeet with one another at their parting faces 4 and 6 respectively toform an entire mold block.

Mold block section 3 has a mounting base 7 which is the region of themold block which secures to the endless track or to a mold block carrier(not shown) on the endless track. An air manifold 9 is provided in themounting base of mold block section 3. Manifold 9 is preferably inconstant communication through the mold tunnel with an outside source ofair pressure which controls or determines the air pressure within themold block. A similar manifold 29 is provided a the base 27 of moldblock section 5.

Returning to mold block section 3, it includes an interior productshaping surface generally indicated at 15. This surface is formed byalternating crests and troughs 17 and 19 respectively. A small slit 21is provided continuously around each of the semi-circular troughs 21 insurface 15 of mold block 3. More than one slit may be provided in eachtrough.

Mold block section 5 has an interior surface 35 identical in shape tosurface 15 and also provided with slits. The slits in surface 35 matewith the slits in surface 15 to form a series of side by side continuousslits around the circular troughs formed when the two mold blocksections meet with one another.

The mold block sections shown in FIG. 2 are used for forming annularlyribbed pipe where the ribs on the pipe are spaced from one another. Aswill be appreciated, these mold block sections can be replaced bymodified mold block sections used for forming helically ribbed pipe inwhich case, rather than having individual separate slits, there would beone continuous slit helically winding around the interior surface of themold block.

Mold block section 3 further includes a plurality of air passages 11through the mold block section. Similar air passages 30 are provided inmold block section 5.

The entrances to the air passages 11 open directly to manifold 9. Theair passages then extend through mold block section 3 diverging toopposite sides of the interior product shaping surface 15. The passagesextend tangentially of the semi-circular product shaping face andterminate at parting face openings 12.

The air passages 30 in mold block section 5 have entrances 31 atmanifold 29 and end openings 32 at the parting face 6 of mold blocksection 5.

When the two mold block sections close with one another, the partingface openings 32 of passages 30 meet with the parting face openings 12of passages 11. This then forms a plurality of air channels completelythrough the mold block.

As will be seen in FIG. 2, there are a plurality of passages to eachside of the product shaping interior surface of each mold block section.These passages are separated from one another lengthwise along each moldblock section.

Mold block section 3 includes a further set of shorter passages 13extending from manifold 9 radially of mold block section 3. A similarset of short passages 33 is provided extending from manifold 29 in moldblock section 5.

Mold block section 3 includes a pair of bores 23 and a further bore 25through the mold block section. Similar bores 37 and 39 are providedthrough mold block section 5. Each of these bores opens to the slitsformed in the interior surfaces of the two mold block sections. In moldblock section 3, passages 11 open onto bores 23 and passages 13 openonto bore 25.

In mold block section 5, passages 30 open onto bores 37 while passages33 open onto bore 39.

As will be understood from the above in mold block section 3, each ofthe passages 11 has openings at the manifold 9, at the bore 23 and atthe parting face of mold block section 3. Passages 13 have openings atthe manifold 9 and at the bore 25. The bores 23 and 25 provide air pathsfrom the passages 11 and 13 respectively to the slits in the interiorsurface of mold block section 3. A similar set up is found in mold blocksection 5, where passages 30 have openings at manifold 29, at bores 37and at the parting face of mold block section 5. The bores 37 and 39provide direct air paths for passages 30 and 33 to the slits provided inthe interior surface 35 of mold block section 5.

The key to the present invention lies in the provision of air flowcontrols which dictate the movement of air in the mold block formed bymold block sections 3 and 5. FIGS. 3 through 6 of the drawings show theprovision of these air flow controllers and the positions that they canassume to provide various different modes of operation of the moldblock.

FIG. 7 of the drawings shows that the lower mold block section 5 isprovided with a further bore 48 which penetrates through the spacedapart air passages 30. Bore 48 is provided between bore 37 and partingface openings 32 of passages 30.

Although FIG. 7 only shows one side of mold block section 5, the otherside of the mold block section has the identical setup.

A rotary valve 49 fits into bore 48 extending across all of the airpassages 30. Valve 49 has a maximum diameter the same as the insidediameter of bore 48. The valve is provided with a series of flats 55along its length and each one of these flats is located in one of theair passages 30. As will be seen in FIG. 8, the valve can be set withits flats parallel to the longitudinal axis of passage 30 to allow airto flow past the valve or it can be turned 90° from the FIG. 8 to theFIG. 9 position where the valve blocks air flow through the passages.

Similar valves 45 are provided in passages 11 and passages 13 of moldblock section 3. However, these valves are located between the upperends of passages 11 which open onto manifold 9 and bores 23 throughwhich the passages 11 pass. The operation of valves 45 is identical tothe operation of valves 49. However, it should be noted that the valves45 and 49 will be operated independently of one another.

FIG. 7a shows an alternate type of valve 57 which is nothing more than aplug which is removed from bore 48 of mold block section 5 to allow airto move in both directions through passages 30. However, when the plugis inserted into bore 48, it blocks the movement of air through thepassages.

Either of the above types of valves is easily workable with the moldblock sections with valve 49 having the benefit that it does not need tobe removed but simply can be turned preferably by using the toolreceiving head 51 of the valve.

The mold block as described above is usable in a number of differentmodes of operation. Some of these modes of operation are shown in FIGS.3 through 6.

Referring specifically to FIG. 3, it will be seen that by keeping boththe of the valves 45 and 49 open and by subjecting the manifolds 9 and29 of the mold block sections 3 and 5 respectively to vacuum, air isdrawn along the slits in the interior faces of the two mold blocksections out of the upper mold block section 3 through the bores 23 and25 and also out of the lower mold block section 5 through the bores 37and 39. Therefore, in this mode of operation vacuum is drawn throughboth mold block sections.

FIG. 4 of the drawings shows a situation in which valves 45 are closedand valves 49 remain open. Manifold 29 of the lower mold block section 5is subject to vacuum and the air is drawn out of the mold block asindicated by the arrows in FIG. 4 from the lower mold block sectiononly. However, it should be noted that because of the mating of theparting face openings of the air passages in the upper and the lowermold block sections, some of the air is initially drawn out from themold cavity through not only the bores in the lower mold block sectionbut also from bores 23 in the upper mold block section. Therefore, eventhough the vacuum is only applied from the lower mold block section, theupper mold block section is still subject to the vacuum ensuring evendistribution of the plastic parison 61 which is used to form the pipecompletely around the interior surface of the cavity within the moldblock.

The mold block of FIG. 4 has the benefit that it does not need to beused with a molding apparatus having vacuum features on both sides ofthe mold tunnel, but rather only requires that vacuum systems need onlybe provided on one side of the mold tunnel substantially reducing costsof the overall molding apparatus.

In the FIG. 5 arrangement, it will be seen that rather than using vacuumforming, blow molding as indicated by the arrows inside of parison 61can be used to force the parison outwardly onto the interior surfaces ofthe mold block sections. In this case, like the setup in FIG. 3, all ofthe valves are left in the air flow position which enables air trappedbetween the parison and the interior surface of the mold block to bereleased outwardly through all of the air passages.

FIG. 6 shows a mode of operation of the mold block which is very uniqueand beneficial. This mode of operation is used for cooling of both thepipe within the moving mold tunnel as well as the mold block sections asthey move along the mold tunnel.

More specifically, in my copending application, I describe how after thepipe is initially shaped within the mold tunnel using any one of theformation methods of FIGS. 3 through 5, there will tend to be shrinkageof the pipe away from the interior wall surfaces of the mold blocksections. This occurs while the pipe is still in the mold tunnel. As aresult, a gap G is produced between the formed pipe and the interiorwall surface of the mold block. The setup of FIG. 6 takes advantage ofthis pipe shrinkage to provide enhanced cooling of both the pipe and themold block sections.

More specifically, valves 49 in the lower mold block section 5 are setto the air blocking position whereas all of the valves in the upper moldblock section are set in the air flow position. Air, which may beambient air or chilled air, is taken from outside of the lower moldblock section 5, is introduced from the base of the lower mold blocksection and along the channels 30 and 33 into the gap G through thebores 37 and 39 respectively. This air then flows around the pipe in thegap G and is withdrawn at bores 23 and 25 out of mold block section 3,the manifold 9 of which is subject to vacuum. Valves 49 being in theblocking position prevent the cooling air from being drawn directlythrough the mold block without going around the pipe.

The cooling air not only has a cooling effect on the pipe butadditionally has a cooling effect on each of the mold block sectionsinitially as it passes through mold block section 5 and then later as itis withdrawn through mold block section 3.

Although various preferred embodiments of the present invention havebeen described in detail, it will be appreciated by those skilled in theart, that variations may be made without departing from the spirit ofthe invention or the scope of the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of operating amold block for use in a moving tunnel where the mold block comprisesfirst and second mold block sections, each of which has a productshaping interior surface and a parting face, each mold block sectionfurther having an air movement passage therein with the passage havingan entrance, a first opening to the product shaping interior surface anda second opening to the parting face, the second opening of the passagein the first mold block section being in communication with the secondopening of the passage in the second mold block section when the moldblock sections are closed at their parting faces with one another andfirst and second air flow controllers moveable independently of oneanother between an air flow and an air blocking position, the first airflow controller being located between the first and second opening inthe passage in the first mold block section, and the second air flowcontroller being located between the entrance and the first opening inthe second mold block section, said method of operating said mold blockbeing selected from the group consisting of a first vacuum forming modein which both of said air flow controllers are set in the air flowposition and in which air is withdrawn from the mold block through bothmold block sections, a second vacuum forming mode in which the first airflow controller is set in the air flow position and the second air flowcontroller is set in the air blocking position and air is withdrawn fromthe mold block through only the first mold block section, a thirdcooling mode of operation in which the first air flow controller is setin the air blocking position and the section air flow controller is setin the air flow position and air to cool the mold block is introduced tothe mold block through the second mold block section and is withdrawnfrom the mold block through the first mold block section, and a fourthblow molding mode of operation in which both air flow controllers areset in the air flow position and air pressure is released from the airblock through both mold block sections.